The present invention relates to an ultrasonic device for measuring the rate of flow of fluid in a duct, particularly for measuring the mass flow rate of air passing along the inlet duct of a heat engine.
As is known, especially in the said application, and when the engine is fed by an electronic fuel injection system, it is particularly important to measure even very short term variations in the flow rate in a sufficiently precise and rapid manner for the purpose of correctly performing the various engine control strategies.
To overcome the disadvantages of slowness in response and of major breakdowns of moving parts, to which measurement devices of mechanical type are subject, ultrasonic measurement devices have been proposed, which are based on the principle of detecting the off-set in the phase difference presented by two ultrasonic frequency signals which are exchanged between respective electroacoustic transducers functioning alternately as transmitter element and receiver element and which are disposed in diametrically opposite positions in the duct itself. The circuit which drives the transducers and processes the signals supplied thereby is necessarily very complex and therefore as well as being relatively expensive can to some extent be subject to breakdowns.